710 PROTOZOOLOGY 



Pearson (1932) and Kudo (1934) reported extensive infections in 

 large open ponds in Indiana and Illinois and Butcher (1941, 1943) 

 noted infections in many yearling trout in hatcheries in 1939 and 

 1940. MacLennan (1935, 1935a, 1937, 1942) observed that the grown 

 trophozoites leave the host epithelium and encyst on the bottom of 

 aquarium; the cytostome is absorbed; the body protoplasm divides 

 into 100-1000 small spherical ciliated cells, 18-22^ in diameter, 

 which presently metamorphose into elongated forms, measuring 

 about 40^ to 10/x. These young ciliates break through the cyst wall 

 and seek new host fish by active swimming. The young ciliates are 

 able to attack the fish integument for at least 96 hours, though their 

 infectivity decreases markedly after 48 hours. 



Sikama (1938) observed a similar organism on 44 species of ma- 

 rine fishes. This ciliate was somewhat smaller in dimensions, meas- 

 uring up to 452m by 360/z, and possessed a macronucleus typically 

 constricted into four beads. Fibrillar structures (ten Kate, 1927). 



Genus Bursella Schmidt. Oval; anterior end broadly and ob- 

 liquely truncate where a large ciliated groove-like pit occurs; ridges 

 of pit contractile; cilia short; macronucleus, spherical to ellipsoidal; 

 several micronuclei; endoplasm reticulated; with symbiotic algae; 

 ectoplasm with trichocysts; fresh water. 



B. spumosa S. 240-560^ long; freshwater pond. 



Genus Spasmostoma Kahl. Somewhat similar to Holophrya; 

 cytostome with flaps which beat alternately; ciliation uniform. 



S. viride K. (Fig. 304, c). Spherical or oval; always with green food 

 vacuoles containing Euglena and allied flagellates; cytostome at 

 anterior end; cytopharynx with trichocysts, which are extensible 

 at the time when food is taken in; cilia on about 20 rows, near cyto- 

 stome somewhat longer; macronucleus round; body 50-75^ long; 

 sapropelic. 



Genus Urotricha Claraparede and Lachmann (Balanitozoon 

 Stokes). Body oval to ellipsoidal or conical; with 1 or more longer 

 caudal cilia; ciliation uniform, except in posterior region which may 

 be without cilia; cytostome at or near anterior end, surrounded by 

 ring of heavier cilia; contractile vacuole, posterior; macronucleus 

 spherical; fresh water. 



U. agilis (Stokes) (Fig. 304, d). Body small; about 15-20m long; 

 swimming as well as leaping movement; standing fresh water with 

 sphagnum. 



U. farcta C. and L. (Fig. 304, e). Body 20-30/x long; fresh water. 

 Kahl considers U. parvula Penard and Balanitozoon gyrans Stokes 

 are identical with this species. 



